Enzyme composition for tissue dissociation

ABSTRACT

An enzyme composition and its use for isolating cells or cell clusters from tissue is disclosed. The composition includes two purified collagenase enzymes and an endoprotease. The ratio of the total FITC casein activity of the enzyme composition to the Wunsch units of activity of the masses of collagenase I and collagenase II is about 85:1 to about 3,900:1.

This application is a continuation of application Ser. No. 08/760,893,filed on Dec. 06, 1996, now U.S. Pat. 5,830,741.

FIELD OF THE INVENTION

This invention relates to compositions for the enzymatic dissociation ofextracellular tissue matrices to allow tissue remodeling and theefficient isolation of viable cells and cell clusters from tissue.

BACKGROUND OF THE INVENTION

The enzymatic dissociation of tissue into individual cells and cellclusters is useful in a wide variety of laboratory, diagnostic andtherapeutic applications. These applications involve the isolation ofmany types of cells for various uses, including microvascularendothelial cells for small diameter synthetic vascular graft seeding,hepatocytes for gene therapy, drug toxicology screening andextracorporeal liver assist devices, chondrocytes for cartilageregeneration, and islets of Langerhans for the treatment ofinsulin-dependent diabetes mellitus. Enzyme treatment works to fragmentextracellular matrix proteins and proteins which maintain cell-to-cellcontact. Since collagen is the principle protein component of tissueultrastructure, the enzyme collagenase has been frequently used toaccomplish the desired tissue disintegration.

Different forms of crude bacterial collagenase derived from Clostridiumhistolyticum are commercially available and are used to dissociate cellsand cell clusters from tissue. These crude collagenases, derived fromcell culture supernatants, typically contain a mixture of proteaseenzymes (exhibiting both collagenolytic and non-specific proteolyticactivities) and non-protease components (e.g., fermentation by-products,media components, pigments, other enzymes such as phospholipase, andendotoxins).

Analysis of commercially-available crude collagenases has shown extremevariations in the concentration and ratios of the protease andnon-protease components. Such compositional variability is reflected aswell in the variability and consequent lot-to-lot unpredictability ofcollagenase product performance in tissue dissociation protocols. Inaddition to this inherent activity variability, each lot of commercialcollagenase loses activity and performance characteristics over time.Finally, in addition to these problems associated with compositionalvariability, the use of crude collagenases in cell harvest/tissuedissociation protocols usually results in less- than-desired results interms of recovery of cell viability, cell number and cell function.These problems are particularly significant where the cells are targetedfor use in transplantation or for monitoring the impact of effectormolecules on cell function. For example, it has been demonstrated thatthe efficacy of islet transplantation is dependent in part on the massof islets and their viability. In addition, the drug detoxificationfunction of recovered hepatocytes is significantly impaired by damage tothe cells occurring during liver tissue dissociation and cell isolation.For most uses of recovered cells it is critical for optimum cellperformance that damage to the recovered cells and cell clusters beminimized.

Skilled practitioners have recognized the importance of theconsistent/predictable activity of protease enzymes used in tissuedissociation protocols for efficacious cellular isolation (i.e.,maintaining cellular integrity, recovering larger cell clusters and morecells or cell clusters). Specifically, the purity of collagenasecompositions and the desirability of the presence of defined amounts ofboth C. histolyticum collagenase class I (collagenase I) and collagenaseclass II (collagenase II) enzymes with at least two neutral proteaseshas been found to influence the efficacy of pancreatic islet isolation.However, there still exists a need for identifying optimized enzymecompositions which provide for rapid dissociation of tissue and recoveryof a greater number of viable cells.

SUMMARY OF THE INVENTION

The present invention provides an enzyme composition prepared bycombining defined masses of purified proteases, including collagenase Iand collagenase II from C. histolyticum and an amount of an endoproteasesuch that the ratio of the total FITC casein units of activity of theenzyme composition to the Wunsch units of activity of the masses ofcollagenase I and collagenase II is about 85:1 to about 3,900:1. Whenused in tissue dissociation protocols for cell isolation the resultingenzyme composition functions to effect improved, more rapid dissociationof extracellular matrices and it allows recovery of higher yields of thedesired cells with improved viability relative to the number andviability of cells harvested using enzyme compositions of the prior art,including crude collagenase compositions.

In another embodiment of this invention there is provided an enzymecomposition consisting essentially of collagenase I and collagenase IIfrom C histolyticum and an endoprotease, wherein the ratio of the massof collagenase II to the mass of collagenase I plus the mass ofcollagenase II in the enzyme composition is about 0.3 to about 0.6. Theresulting enzyme composition is also an improvement over previouslyknown compositions because of its ability to more rapidly dissociateextracellular tissue matrices and allow recovery of a larger number ofviable cells.

This invention also provides a method of preparing an enzyme compositionadapted for isolating living cells from tissue which includes the stepof combining known masses of collagenase I and collagenase II from C.histolyticum and an amount of an endoprotease sufficient to raise thetotal FITC casein activity of the enzyme composition to a level suchthat the ratio of the total FITC casein activity of the enzymecomposition to the total Wunsch unit activity of the masses ofcollagenase I and collagenase II in the enzyme composition is about 85:1to about 3,900:1.

DETAILED DESCRIPTION OF THE INVENTION

This invention is based on the discovery that collagenase I andcollagenase II from C. histolyticum may be combined with defined amountsof an endoprotease to provide a novel enzyme composition having activityprofiles optimal for isolating cells from donor organ tissue. Morespecifically, it has been discovered that optimal enzymatic degradationof extracellular tissue matrices and concomitant efficient liberation ofviable cells and cell clusters from organ tissue can be achieved byusing a collagenase enzyme composition prepared by adjusting thecomponents of the composition so that the ratio of the total FITC caseinactivity of the enzyme composition to the Wunsch units of activity ofthe masses of collagenase I and collagenase II in the composition isabout 85:1 to about 3,900:1 and is preferably about 130:1 to about1,400:1. In one embodiment of the invention, there is provided an enzymecomposition useful for efficient dissociation of rat liver tissue toprovide a high yield of hepatocytes. That enzyme composition includesamounts of collagenase I and collagenase II from C. histolyticum and anendoprotease such that the ratio of the total FITC casein activity ofthe enzyme composition to the Wunsch units of activity of the masses ofcollagenase I and collagenase II in the composition is about 250:1 toabout 600:1, with an average ratio of about 400:1.

Another aspect of the present invention is optimizing mass ratios of thetwo component collagenase enzymes in enzyme compositions of thisinvention consisting essentially of collagenase I, collagenase II and anendoprotease. The optimal mass ratio of collagenase II to the totalcollagenase in the composition, collagenase II/(collagenase I+collagenase II), is about 0.3 to about 0.6. When collagenase I andcollagenase II from C. histolyticum are combined in this mass ratio withan endoprotease, the resulting enzyme composition is particularly usefulto recover cells and cell clusters from tissue samples in greaternumber, with higher viability, and with improved reproducibility overtissue dissociation protocols using previously known collagenase enzymecompositions. In one enzyme composition embodiment of this inventionuseful for dissociating rat liver, the mass ratio of collagenase II tothe total collagenase in the composition is about 0.35 to about 0.45.

The enzyme compositions of the present invention include bothcollagenase I and collagenase II from C. histolyticum. Collagenase I andcollagenase II are purified from C. histolyticum crude collagenase by avariety of methods known to those skilled in the art, including dyeligand affinity chromatography, heparin affinity chromatography,ammonium sulfate precipitation, hydroxylapatite chromatography, sizeexclusion chromatography, ion exchange chromatography, and metalchelation chromatography. Crude collagenase is commercially availablefrom many sources (e.g., Collagenase P from Boehringer MannheimCorporation).

The endoprotease component of the present enzyme composition can be anyendoprotease, including a serine protease (e.g., trypsin, chymotrypsin,elastase), a cysteine protease (e.g., papain, chymopapain) and ispreferably a neutral protease (e.g., C. histolyticum neutral protease,dispase, or thermolysin (all EC 3.4.24.4). (EC stands for EnzymeCommission classification. EC 3.4.24.4 is the classification formicrobial metalloproteinases.)

For dissociation of a 6 to 12 gram rat liver to recover hepatocytes, theactivity of the masses of collagenase I and collagenase II in the enzymecomposition is about 7.7 to about 62.7 Wunsch units, preferably about15.1 to about 52.6 Wunsch units, and more preferably about 24 to about33 Wunsch units with an average activity of about 30 Wunsch units. Thetotal FITC casein activity of this enzyme composition is about 5,500 toabout 29,700 FITC casein units, preferably about 7,000 to about 22,000FITC casein units, and more preferably about 8,500 to about 14,500 FITCcasein units with an average activity of about 12,000 FITC casein units.Accordingly, the ratio range of FITC casein units of the composition toWunsch units of the composition is 5,500/62.7 to 29,700/7.7 or about85:1 to about 3,900:1, preferably 7,000/52.6 to 22,000/15.1 or about130:1 to about 1,400:1, and more preferably 8,500/33 to 14,500/24 orabout 250:1 to about 600:1 with an average activity ratio of 12,000/30or about 400:1.

In addition to the dissociation of liver for isolation of hepatocytes,the above composition is useful for the dissociation of epidermal fatfor the isolation of microvascular endothelial cells. The abovecomposition is also expected to be useful for dissociating pancreastissue, topical treatment for burn and ulcer clearing and for woundhealing, treatment of Peyronie's disease and reformation of abnormal orherniated discs. In general, the composition of the present invention isuseful for any application where the removal of cells or modification ofan extracellular matrix are desired.

For some applications, it may be preferred that the enzyme compositionbe substantially free of endotoxins. It may also be desirable for theenzyme composition to be substantially free of the enzyme clostripain,although generally clostripain does not seem to affect performance ofthe enzyme composition. These undesirable components, which are bothpresent in crude collagenase obtained from C. histolylicum, can beseparated from the purified collagenase I and II components using one ormore of the purification methods described above. "Substantially free"as used herein to describe this invention means that effort is or hasbeen made to exclude referenced impurity from the composition and thatsuch impurity, if present at all in the composition, is present in buttrace amounts, typically less than 2% by weight, more typically lessthan 1% by weight and in any event less than an amount which wouldaffect the aggregate functionality of the composition.

Enzyme compositions of this invention may be prepared by mixing either aspecific number of activity units (i.e., Wunsch units of collagenase Iand collagenase II) or specific masses of the preferably purifiedenzymes. Following are enzyme assays for collagenase, neutral proteaseand clostripain that were used to define the specific activities of thepurified collagenase components as well as the total activity (FITC) ofthe entire enzyme composition. Those skilled in the art will recognizethat enzyme assays other than those disclosed below may also be used todefine and prepare functionally equivalent enzyme compositions.

Collagenase activity assay

Collagenase activity was measured using a synthetic peptide substrateaccording to the method of Wunsch & Heidrich (Z. Physiol Chem. 1963;333:149). This is a standard method well known to those skilled in theart of collagenase purification. The measured activity of collagenase Iusing the Wunsch peptide as a substrate typically ranged from 0.2 to 0.6units (U)/milligram (mg) and was more typically 0.3 to 0.5 U/mg. Themeasured activity of collagenase II using the Wunsch peptide as asubstrate typically ranged from 9.5 to 13.5 U/mg and was more typically11 to 13 U/mg. One Wunsch unit (U) of activity is defined by thehydrolysis of 1 micromole (μmol) peptide per minute at 25°C., pH 7.1. Adescription of the test procedure used for the collagenase activityassay is given below. Sample Dilution Buffer (100 millimoles (mM)/liter(l) tris-(hydroxymethyl)-aminomethane (Tris). pH 7.1): 1.21 gram (g)Tris was dissolved in deionized (DI) water. The pH was adjusted to 7.1with 1.0 Normal (N) hydrochloric acid (HCl) and the volume was adjustedto 100 milliliters (ml) with DI water.

PZ-Pro-Leu-Gly-Pro-D-Arg substrate: Each blank or test sample wasassayed in duplicate. Total amount of substrate needed for assay =2 mgof substrate for each test performed, plus 2 mg of substrate extra. (Forexample, 2 samples tested in duplicate +duplicate blank tubes =6 assaytubes. The target amount of substrate needed is 14.0 mg.) The totalamount of substrate weighed out was divided by 50 to determine thenumber of milliliters of methanol needed to dissolve the substrate. Thecalculated amount of methanol was added to the substrate. The substratewas mixed thoroughly by vortexing until totally dissolved. SampleDilution Buffer was added to the dissolved substrate to a final volumeso that the concentration of substrate was 1 mg/ml.

100 mM/l Calcium Chloride (CaCl₂): 1.47g CaCl₂, Formula Weight (FW) 147,was dissolved in DI water. The volume was adjusted to 100 ml with DIwater.

25 mM/l Citric Acid: 0.525g Citric acid, FW 210..l, was dissolved in DIwater. The volume was adjusted to 100 ml with DI water.

Assay Mixture. 2.0 ml of PZ-Pro-Leu-Gly-Pro-D-Arg Substrate and 0.4 ml100 mM

CaCl₂ were added to 12×75 millimeter (mm) test tubes and capped. Theassay mixtures were allowed to equilibrate in a water bath to 25° C.before beginning the assay. One tube was prepared for each duplicateblank or sample tested.

Extraction Mixture: 5.0 ml of ethyl acetate and 1.0 ml of 25 mM/l citricacid were added to 16×125 mm test tubes. Each tube was capped. One tubewas prepared for each duplicate blank or sample tested.

Drying tubes: 0.35 to 0.4 g anhydrous sodium sulfate was added to 16×125mm test tubes. Each tube was capped. One tube was prepared for eachduplicate blank or sample tested.

Assay Procedure: All concentrated and diluted enzyme samples were keptat 2° C. to 8° C. until added to the substrate. A sample of either theentire enzyme composition or one of its components (e.g., collagenase I,collagenase II, or neutral protease) was diluted with Sample DilutionBuffer to a concentration range of 0.05 to 0.8 mg/ml, depending uponestimated sample activity. The assay incubation time was started after100 microliters (μl) of blank control (Sample Dilution Buffer was usedas a blank) was added to the first tube of Assay Mixture. The AssayMixture was then capped, mixed thoroughly, and placed in a 25° C. waterbath. At 60 second intervals, 100 μl of the next blank or test samplewas added to a tube of Assay Mixture in the same manner. Each AssayMixture was incubated at 25° C. for 15 minutes (min) from the time theblank or test sample was added. After 15 min of incubation, 0.5 ml ofthe first blank Assay Mixture was transferred to a tube containingExtraction Mixture. The Extraction Mixture tube was capped and mixedthoroughly by vortexing for 20 seconds. At 60 second intervals, theremaining blank or test samples were transferred to Extraction Mixturetubes and mixed in the same manner, so that total incubation time foreach sample was 15 min. 3 ml of the organic phase (top) from eachExtraction Mixture was pipetted into a Drying Tube. The Drying Tubeswere capped, mixed and incubated at room temperature in a fume hood for30 to 60 min. The tubes were mixed again during this period. The organicphase was pipetted into quartz cuvettes and, using atemperature-controlled spectrophotometer at 25° C., the absorbance wasread at 320 nanometers (nm) for each blank and sample.

Calculations: A₃₂₀ =Average absorbance of sample --Average absorbance ofbuffer blank. Activity (U/ml)=(A₃₂₀ ×2.5×5×DilutionFactor)/(21×0.10×0.5×15). Simplified, U/ml=A₃₂₀ ×0.79×Dilution Factor.The U/mg specific activity was calculated for each sample by thefollowing calculation: specific activity (U/mg)=(U/ml)/(mg/ml).

Neutral Protease Activity Assay

Neutral protease activity was measured by the liberation oftrichloroacetic acid (TCA) soluble fluorescent peptides from thesubstrate FITC-casein according to a modified version of the method ofTwining (Anal. Biochem.1984; 143:30). Fluorescent peptides werequantified using an excitation wavelength of 491 nm and an emissionwavelength of 525 nm. The range of measured FITC-casein specificactivity for the neutral protease dispase was typically 600 to 1400 U/mgand was more typically 1100 to 1400 U/mg. The range of measuredFITC-casein specific activity for the neutral protease thermolysin wastypically 3000 to 6500 U/mg and was more typically 3500 to 6000 U/mg.One unit of activity generates 100,000 fluorescence units (counts persecond) corrected for background per minute at 37° C., pH 7.5. Adescription of the test procedure used for the neutral protease activityassay is given below.

Sample Dilution Buffer (100 mM/l Tris. 10 mM/l CaCl₂, pH 7.5): 6.06gTris and 0.74 g CaCl₂ were dissolved in DI water. The pH was adjusted to7.5 with 1.0N HCI and the volume adjusted to 500 ml with DI water.

FITC-Casein Substrate Solution (0.25% w/v): 50.0 mg FITC-casein wasdissolved in the Sample Dilution Buffer. The volume was adjusted to 20.0ml with Sample Dilution Buffer. Quenching Solution (5.0% w/v): 5.0 g ofTrichloroacetic Acid was dissolved in DI water. The volume was adjustedto 100 ml with DI water. Neutralization Solution (500 mM/l Tris: pH8.5): 30.3 g Tris was dissolved in DI water. The pH was adjusted to 8.5with 1.0N HCI and the volume was adjusted to 500ml with DI water.

Assay Procedure: All concentrated and diluted enzyme samples were keptat 2° C. to 8° C. until added to the substrate. Each blank or testsample was assayed in duplicate. A sample of either the entire enzymecomposition or one of its components (e.g., collagenase I, collagenaseII, or neutral protease) was diluted with Sample Dilution Buffer to aconcentration range of 1 to 50 micrograms (μg)/ml, depending uponestimated sample activity. 10 μl of the diluted samples were added to 40μl of FITC-casein Substrate Solution in 1.5 ml Eppendorf tubes (theSample Dilution Buffer was used as a blank control) and incubated for 45min with shaking at 37° C. in a water bath. The tubes were removed fromthe water bath and 120 μl of the Quenching Solution was added. The tubeswere vortexed and left at room temperature for at least 60 min. Thetubes were then centrifuged in a microcentrifuge at 14,000 rpm for 2min. 50 μl of the supernatant was removed and added to 2ml ofNeutralization Buffer in a cuvette. The cuvette was capped and invertedto mix the solution. Fluorescence was then measured (excitationwavelength 491 nm, emission wavelength 525 nm, slit width 0.2 nm).

Calculations: CPS =Average enzyme sample fluorescence --Average bufferblank fluorescence. Activity (U/ml)=(CPS×0.17 ml ×Dilution factor)/(0.05ml×0.01 ml ×45 min. ×100,000). Simplified, U/ml =CPS ×0.0000755×Dilution factor. The linear range for the SPEX fluorimeter is from 4000to 100,000 CPS.

The substrate casein used in the assay for neutral proteases describedabove can also act as a general substrate for a wide variety of proteaseactivities including trypsin, clostripain, dispase, thermolysin, andmany others. The preferred ranges for FITC casein activity of the totalenzyme composition described herein were measured and defined as unitsof activity of the final enzyme composition and were not the actualunits of the neutral protease components measured alone prior to mixing.

Clostripain Activity Assay

Clostripain activity was measured by the esterolysis ofN-benzoyl-L-arginine ethyl ester (BAEE) according to a modification ofthe method of Whitaker and Bender (J. Am. Chem. Soc. 1965; 87:2728).Clostripain is a cysteine protease activated by reducing agents such asdithiothreitol (DTT). Measured clostripain activity is the differencebetween DTT-activated enzyme and non-DTT-treated enzyme. The activitiesdescribed were generated using 1.8 mM BAEE. One unit is defined as thehydrolysis of 1 μmol BAEE per min at 25° C., pH 7.6. A description ofthe test procedure used for the clostripain activity assay is givenbelow.

Phosphate Buffer (75 mM/l): 1.17 g sodium phosphate, monobasic (NaH₂PO₄) was dissolved in DI water. The volume was adjusted to 100 ml withDI water and labeled "solution A".1.07 g sodium phosphate, dibasic (Na₂HPO₄) was dissolved in DI water. The volume was adjusted to 100 ml withDI water and labeled "solution B". The pH value of solution B wasadjusted to 7.6 with solution A.

DTT Solution (7.5 mM/l): 28.9 mg dithiothreitol (DTT) was dissolved inDI water and the volume was adjusted to 25 ml with DI water.

BAEE Solution (1.8 mM/l): 15.4 mg BAEE was dissolved in DI water and thevolume was adjusted to 25 ml with DI water.

10×Activating Solution (10 mM/l calcium acetate. 25 mM/l DTT): 17.6 mgcalcium acetate and 38.6 mg DTT was dissolved in DI water and the volumewas adjusted to 10.0 ml with DI water.

10×Blank Solution (10 mM/l calcium acetate): 17.6 mg calcium acetate wasdissolved in RO/DI water and the volume was adjusted to 10.0 ml with DIwater.

Sample Preparation: All concentrated and diluted enzyme samples werekept at 2° C. to 8° C. until added to the substrate. Collagenase I wasdiluted with a combination of 10×Activation Solution and DI water sothat the final sample concentration was 0.15 mg/ml in 1×ActivationSolution. (For example, to dilute a 26.7 mg/ml collagenase I sample to0.15 mg/ml for assay, mix 10 μl of the 26.7 mg/ml collagenase I samplewith 178 μl of 10×Activating Solution plus 1592 μI DI water.)Collagenase ll was diluted with a combination of 10×Activation Solutionand DI water so that the final sample concentration was 0.4 mg/ml in1×Activation Solution. (For example, to dilute a 31.2 mg/ml collagenaseII sample to 0.4 mg/ml for assay, mix 10 μl of the 31.2 mg/mlcollagenase II sample with 78 μof 10×Activating Solution plus 692 μl DIwater.) The samples were then incubated for 4.5 hours at roomtemperature.

Trypsin Blank Preparation: Trypsin blanks were prepared by repeating thesample dilutions using 10×Blank Solution in place of 10×ActivatingSolution and 1×Blank Solution in place of 1×Activating Solution.

Spectrophotometric Assay (wavelength 253 nm, final volume 0.93 ml.temperature 25°C.): A trypsin blank mixture and an activated samplemixture were prepared by mixing the following:

    ______________________________________                            Activated sample                Trypsin blank mixture                            mixture    ______________________________________    BAEE Substrate                  5.0 ml        5.0 ml    75 mM/l phosphate buffer                  5.0 ml        5.0 ml    pH 7.6    DI water      5.0 ml        --    7.5 mM/l DTT Solution                  --            5.0 ml    ______________________________________

Four quartz cuvettes were placed in the spectrophotometer. 0.9 ml of thetrypsin blank mixture was pipetted into each of the first two cuvettes.0.9 ml of the activated sample mixture was pipetted into each of theremaining two cuvettes. The absorbance was read for 1.5 min to establisha blank rate (the blank rate should not exceed 0.01 delta (Δ) A₂₅₃/min). The reaction was then started by pipetting 0.03 ml of the dilutedTrypsin Blank Preparation into the two trypsin blank cuvettes and 0.03ml of the diluted Sample Preparation into the two activated samplecuvettes and mixing thoroughly. Each cuvette was read for 1.5 min todetermine the reaction rate. (The ΔA₂₅₃ /min should be between 0.007 and0.040.)

Calculation: For each sample, the U/ml activity was calculated asfollows: U/ml= (ΔA/minute)×(dilution factor)×(0.93)×(1000)!/(1150)×(0.03)!where ΔA/minute =ΔA₂₅₃ /min sample -ΔA₂₅₃ /min blank.Simplified, U/ml =(ΔA/minute)×(dilution factor)×(26.96). The U/mgspecific activity was calculated for each sample by the followingcalculation: specific activity (U/mg)=(U/ml)/(mg/ml).

EXAMPLE 1: PURIFICATION OF COLLAGENASE I AND COLLAGENASE II FROM CRUDEBACTERIAL COLLAGENASE

Commercially available crude bacterial collagenase (Collagenase P,Boehringer Mannheim Corporation) was used as the starting material.Three dye ligand affinity chromatography supports from Amicon were foundto perform acceptably. These supports were MATREX (registered trademark,W.R. Grace & Co.) Gel Blue A, MATREX Gel Red A, and MATREX Gel Green A.Comparable products from other suppliers were found to perform in asimilar manner. For maximum recovery of activity, all purification stepswere performed at 2° C. to 8°C.

The crude bacterial collagenase and the chosen support were equilibratedagainst a low ionic strength calcium-containing buffer at a pH between6.0 to 7.5. For the best combination of purification efficiency, enzymestability and resin capacity a pH range of 6.5 to 7.0 is preferable. Forthese chromatographies either 20 mM 4- 2- hydroxyethyl!- 1- piperazineethanesulfonic acid (HEPES) or 20 mMbis-(2-hydroxyethyl)-imino!-tris-(hydroxymethyl)-methane (BIS-Tris), 1mM calcium chloride pH 7.0 buffers were used for resin and enzymeequilibration. The crude bacterial collagenase was dissolved bysuspending the lyophilized starting material in the selectedequilibration buffer at a sample concentration of about 40 mg/ml.Concentrations of 1 to 100 mg/ml have been used with concentrationsaround 40 mg/ml having the best combination of enzyme stability andshort sample loading times. Insoluble material can be removed bycentrifugation and/or filtration through cellulose, cellulose acetate,polyethersulfone or other low protein binding membranes.

The clarified sample was applied to the resin at flow rates ranging from0.1 to 2.0 centimeters (cm)/min. The purification is insensitive to flowrate so that flow rate which best fits the production schedule is used.Depending on the lot of resin, 10 to 15 mg of enzyme can be bound to theRed A and Green A resins which translates to a binding capacity of 20 to40 mg of collagenase P per milliliter of these supports. The Blue Aresin has about 1/2 of this capacity. After the sample has been loadedonto the column the unretained material is washed from the column by theapplication of equilibration buffer. Usually two to three column volumesof buffer is sufficient for this task.

The bound enzymes were recovered by elution from the resin using a saltand/or pH gradient. Elution buffers comprising 20 mM HEPES, 1 mM calciumchloride and 400 mM sodium chloride pH 7.5 or 20 mM Tris, 1 mM calciumchloride and 150 mM sodium chloride pH 9.0 were sufficient to recoverthe bulk of the bound proteolytic activity.

The dye ligand affinity purified collagenase enzyme mixture was furtherpurified by strong cation exchange chromatography on SP Sepharose FastFlow resin (registered trademark, Pharmacia, Inc.). Before use the resinwas converted from the sodium form to the calcium form. This wasaccomplished by washing the resin with excess calcium chloride solution.A 1/2 column volume of 500 mM calcium chloride solution was sufficientto convert the packed resin into the calcium form. The packed calciumform resin and the dye ligand affinity purified enzyme solution wereequilibrated against a low ionic strength calcium containing buffermaintained at a pH of between 6.5 and 7.5. For these chromatographies 20mM HEPES, 5 mM calcium chloride pH 7.0 buffer was used forequilibration. The equilibrated dye ligand affinity purified enzymemixture was applied to the calcium form SP Sepharose FF column at flowrates up to 8 cm/min. For most purifications a flow rate of 2 cm/min ismost convenient for speed and ease of process control. After the samplewas applied the collagenase enzymes were eluted by the application ofequilibration buffer. Usually about two column volumes of buffer weresufficient to elute all of the collagenase enzymes from the column. Oncethe collagenase enzymes were eluted from the column the bound proteins(predominantly clostripain along with several non-protease proteins) canbe eluted using a 5 to 100 mM calcium chloride gradient. This wasaccomplished using a 10 to 15 column volume linear gradient to recoverthe purified clostripain or by a step gradient to clean the column forreuse. On average one to two milligrams of clostripain were bound permilliliter of resin. It is important to saturate this resin with calciumbecause if this is not done the resin will remove calcium from theenzymes in the preparation which will result in increased degradation ofthe enzymes and poorer recoveries. It is expected that other strongcation exchange resins should perform in a similar manner as this resin.

The flow through fraction from the calcium saturated SP Sepharose FFcolumn, which contained the collagenase enzymes and the clostridialneutral protease, was purified by anion exchange chromatography oneither diethyl aminoethyl (DEAE) or trimethyl aminoethyl (Q) SepharoseFast Flow (Pharmacia). Both the support and the enzyme sample wereequilibrated against a low ionic strength calcium containing buffer witha pH of between 6.5 to 9.0. Within this pH range both resins yieldedsimilar purification efficiencies and recoveries. However, because ofits simpler regeneration and equilibration protocols, the Q Sepharose FFsupport was used. For these chromatographies 5 mM HEPES, 1 mNM calciumchloride pH 7.5 buffer was used. The equilibrated collagenase enzymepool was applied to the equilibrated resin at flow rates up to 8 cm/min(usually at 1 to 2 cm/min). On average 20 to 50 mg of enzyme mixturewere applied per ml of resin. Once the mixture was applied to the resinthe enzymes were eluted by a 1 to 100 mM calcium chloride lineargradient. A 20 to 30 column volume gradient was used. The collagenase IIenzyme eluted at about 15 to 20 mM calcium, the collagenase I eluted atabout 30 to 35 mM calcium, and the neutral protease at about 60 to 70 mMcalcium.

The recovered enzymes were equilibrated against 5 mM HEPES, 1 mM calciumchloride pH 7.5 buffer and stored frozen at or below -20°C. Whenpurified in this manner and kept under these conditions the collagenaseenzymes can be kept for at least two years without evidence of activityloss.

Collagenase I and II prepared in this manner have been found to besubstantially free of clostripain. In our experience material preparedin this way has less than 3 BAEE units of clostripain activity andusually have one or less units of activity. This translates to a veryhigh level of purity (98 to 99%) for both coliagenase components. Table1 below shows the typical enzyme activities of the purified enzymecomponents.

                  TABLE 1    ______________________________________    Typical enzyme activities of purified enzyme components                Wunsch    BAEE       FITC casein    Enzyme      Activity  Activity   Activity    ______________________________________    collagenase 0.2-0.6    I           U/mg    collagenase 9.5-13.5    II          U/mg    clostripain           70-140                          U/mg    thermolysin                      3000-6500                                     U/mg    dispase                          600-1400                                     U/mg    ______________________________________

EXAMPLE 2: PREPARATION OF AN ENZYME COMPOSITION FOR THE ISOLATION OFHEPATOCYTES FROM LIVER

Collagenase I and II, which have very high solubilities, were preparedand stored as frozen liquids as described above in Example 1. However,thermolysin has a much lower solubility and is much harder to get intosolution, especially in concentrations greater than 2.0 mg/ml. Toaccomplish a reproducible solubilization of this enzyme a modificationof the procedure presented by Matsubra (Methods in Enzymology v. 19pp.642-651) was used. The desired mass of dry thermolysin (BoehringerMannheim Corporation, Biochemicals cat. #161586) was placed in anappropriately sized container. Sufficient high purity water was added toprepare an 8 mg/ml thermolysin suspension. After mixing in an ice bathto hydrate the thermolysin crystals, sufficient cold dilute sodiumhydroxide solution was added to adjust the pH to about 10.5 Ifnecessary, the pH can be increased to 11.5 to insure completesolubilization. When solubilization was complete the solution had alight yellow to light tan color. The pH of this solution was thenlowered to 8.5 using a dilute acetic acid solution. HEPES free acid alsoworks well and is compatible with the buffer solution. After thissolubilization process a thermolysin solution with a proteinconcentration of 5 to 6 mg/ml can be maintained for at least severalhours at 0 to 8°C.

Enzyme compositions were prepared by mixing specific masses of eachenzyme. The mass of each enzyme was determined based upon its absorbanceat 280 nanometers. For collagenase I and II, a 1.0 mg/ml solution willhave an absorbance of 1.4 absorbance units (AU) and a 1.0 mg/mlthermolysin solution will have an absorbance of 1.1 AU. Using thesevalues, solutions of each component were prepared and the calculatednumber of absorbance units for each component were blended to preparethe desired mixtures.

The collagenase I and II samples from Example 1 above were thawed. (Alloperations should be performed at 0 to 8° C. to maximize enzymestability.) A sample of collagenase I enzyme was prepared that contained3.48 mg of protein (4.87 AU). To this sample was added a sample ofcollagenase II enzyme that contained 2.32 mg of protein (3.25 AU). Tothis mixture of collagenase I and II, a volume of thermolysin solutionwas added that provided 1.82 mg of this enzyme (2.00 AU) and mixed well.

Once blended the enzyme composition can be kept in an ice bath forseveral hours without loss of activity. However, it is recommended forlonger term storage that the composition be kept at -20° C. or lower asa frozen liquid or as a lyophilizate. Prepared in this way these blendsare stable for several years. For a 6 to 12 gram liver the masses ofenzymes shown in Table 2 below provided an optimal mixture forhepatocyte isolation.

                  TABLE 2    ______________________________________    Enzyme Composition For Rat Liver Dissociation                         Absorbance  Total                Weig     units/milligr                                     absorbance    Enzyme      ht       am          units    ______________________________________    collagenase 3.48     1.4 AU/mg   4.87 AU    I           mg    collagenase 2.32     1.4 AU/mg   3.25 AU    II          mg    thermolysin 1.82     1.1 AU/mg   2.00 AU                mg    ______________________________________

For the enzyme composition described above in Table 2, collagenase Icontributed about 0.7 to about 1.7 Wunsch units of collagenase activityand collagenase II contributed about 23.2 to about 31 Wunsch units ofactivity. Because thermolysin provided no significant Wunsch activity,the total composition yielded about 24 to about 33 Wunsch units ofactivity with an average activity of about 30 Wunsch units. The totalcomposition had about 8,500 to about 14,500 FITC casein units ofactivity with an average activity of about 12,000 FITC casein units.Accordingly, the ratio range of FITC casein units of the composition toWunsch units of the composition is 8,500/33 to 14,500/24 or about 250:1to about 600:1 with an average activity ratio of 12,000/30 or about400:1.

The enzyme composition described above for dissociation of rat liver isexpected to perform acceptably for other tissue types as well. As willbe apparent to those skilled in the art, some modification may benecessary to optimize the purified enzyme mixture for dissociatingspecific tissue types, e.g. tissues which contain more collagen mayrequire increased collagenase activity and tissues which contain morenon-collagen proteins may require increased protease activity.Similarly, larger or smaller tissue samples might necessitatecorresponding adjustments in enzyme activity.

EXAMPLE 3: DIGESTION OF RAT LIVER FOR THE ISOLATION OF HEPATOCYTES

Purified enzyme composition combinations were tested by their ability todissociate rat liver into free hepatocytes. Minor modifications of theprocedures of Seglen were used for the evaluations (Seglen, Exp. CellRes. 82, pp.391-398(1973)). The buffers described below were used in theorgan dissociation. All buffers were prepared using high purity waterand passed through a 0.2 micron filter to insure sterility.

Perfusion Buffer: 8.3 g sodium chloride, 0.5 g potassium chloride and2.4 g HEPES were added to 800 ml water. After solution was complete thepH was adjusted to 7.4 and the volume brought to 1,000 ml.

Digestion Buffer: 3.9 g sodium chloride, 0.5 g potassium chloride, 0.7 gcalcium chloride dihydrate and 24 g HEPES were added to 800 ml water.After solution was complete the pH was adjusted to 7.6 and the volumebrought to 1,000 ml.

Suspension Buffer: 4.0 g sodium chloride, 0.4 g potassium chloride, 7.2g HEPES, 0.18 g calcium chloride dihydrate, 0.15 g potassium phosphate,0.1 g sodium sulfate, 0.13 g magnesium chloride hexahydrate, 6.9 g (2- {tris-(hydroxymethyl) -methyl!-amino}-ethanesulfonic acid)(TES), 6.5 g {Ntris-(hydroxymethyl)-methyl!-glycine}(TRICINE) and 2.1 g sodiumhydroxide were added to 800 ml water. After solution was complete the pHwas adjusted to 7.6 and the volume brought to 1,000 ml.

Wash Buffer: 8.3 g sodium chloride, 0.5 g potassium chloride, 2.4 gHEPES and 0.18 g calcium chloride dihydrate were added to 800 ml water.After solution was complete the pH was adjusted to 7.4 and the volumebrought to 1,000 ml.

Male Wistar rats (150 to 200 g) were anesthetized using I.P. injectionsof pentabarbitol (10 mg/100 g body weight). The abdominal cavity wasopened and the inferior vena cava cannulated between the liver andkidney. The vena cava was ligated above the liver and the portal veinwas cut or cannulated to allow for reflux from the liver. The liver wasperfused for at least five minutes with perfusion buffer at a flow rateof 30 ml/min. The enzyme composition from example 2 above was dissolvedin 300 ml of digestion solution and incubated at 37° C. until warm. Theliver was then dissociated by passing the digestion solution through theorgan at a flow rate of 30 ml/min until the organ softened. Thedigestion time was noted.

The softened organ was removed and carefully pulled apart in suspensionbuffer which was pre-gassed with 95% oxygen and 5% carbon dioxide. Anyremaining tissue was cut into small pieces and any blood vessels andmembranes were removed. The tissue suspension was brought to a finalvolume of 150 ml with suspension buffer and incubated with gentlestirring at 37° C. for 25 min to disperse the hepatocytes. After removalof tissue chunks by filtration the hepatocytes were pelleted bycentrifugation at 20×G for 5 minutes at 4° C. The non-hepatocyte cells,damaged hepatocytes, and cell debris were located in the supernatant andremoved by aspiration and discarded. The hepatocytes were washed andcentrifuged at least two additional times with cold wash solution. Finalcell count and % viability were determined. Four million hepatocyteswere plated on 60 ml diameter collagen coated culture plates andincubated at 37° C. in 95% air and 5% carbon dioxide at 95% relativehumidity. Function assays were performed at appropriate time intervals.

EXAMPLE 4: DIGESTION OF RAT EPIDERMAL FAT FOR THE ISOLATION OFMICROVASCULAR ENDOTHELIAL CELLS

An enzyme composition containing 2.32 mg collagenase II, 3.48 mgcollagenase I and 1.82 mg thermolysin was used to dissociate samples ofrat fat pad tissue for the purpose of recovering microvascular cells.The procedure used was a minor modification of the procedure of Rodbell(J. Biol. Chem., v. 239, pp. 375 (1964)). The preferred blendcomposition was reconstituted in 20 ml of physiological phosphatebuffered saline (PBS) solution containing 1.0 mg/ml of fatty acid freebovine serum albumin (BSA) and sterilized through a 0.2 micron celluloseacetate filter. Four finely minced epididymal fat pads (fat volumeaverages 3 to 5 ml) from 8 to 10 week old rats were placed in 10 ml ofthe enzyme blend solution. Digestion was performed at 37° C. in ashaking water bath for 10 to 15 min. Cells were recovered bycentrifugation for four minutes at 700×G. Floating fat and enzyme blendsolutions were aspirated and discarded. The endothelial cell pellet wastwice suspended in PBS buffer containing 1.0 mg/ml BSA and the cellsrecovered by centrifugation for four minutes at 700×G with a finalcentrifugation in plain PBS buffer. The cells were then ready forcounting, viability testing, culture or additional fractionation.

What is claimed is:
 1. An enzyme composition prepared by combiningdefined masses of purified proteases comprising collagenase I andcollagenase II from Clostridium histolyticum and an endoprotease,wherein the ratio of the mass of collagenase II to the mass ofcollagenase I plus the mass of the collagenase II in the composition isabout 0.3 to about 0.6 and wherein the ratio of the total FITC caseinactivity of the enzyme composition to the total Wunsch units of activityof the masses of collagenase I and collagenase II in the composition isabout 130:1 to about 1400:1.
 2. The enzyme composition of claim 1wherein the endoprotease is a neutral protease.
 3. The enzymecomposition of claim 2 wherein the neutral protease is selected from thegroup consisting of thermolysin, dispase and Clostridium histolyticumneutral protease.
 4. The enzyme composition of claim 2 wherein theneutral protease is thermolysin.
 5. The enzyme composition of claim 1wherein the ratio of the mass of collagenase II to the mass ofcollagenase I plus the mass of the collagenase II in the composition isabout 0.35 to about 0.45.
 6. The enzyme composition of claim 1 whereinthe composition is substantially free of endotoxins.
 7. A method ofpreparing an enzyme composition adapted for isolating living cells fromtissue, said method comprising the steps of combining known masses ofchromatographically purified collagenase I and collagenase II fromClostridium histolyticum, wherein the ratio of the mass of collagenaseII to the mass of collagenase I plus the mass of the collagenase II inthe composition is about 0.3 to about 0.6, and adding an amount of anendoprotease sufficient to raise the total FITC casein activity of theenzyme composition to a level such that the ratio of the total FITCcasein activity of the enzyme composition to the total Wunsch unitactivity of the masses of purified collagenase I and collagenase II inthe enzyme composition is about 130:1 to about 1,400:1.
 8. The method ofclaim 7, wherein the endoprotease is a neutral protease.
 9. The methodof claim 8 wherein the neutral protease is selected from the groupconsisting of thermolysin, dispase, and Clostridium histolyticum neutralprotease.
 10. The method of claim 8 wherein the neutral protease isthermolysin.
 11. The method of claim 10 wherein the ratio of the mass ofcollagenase II to the mass of collagenase I plus the mass of thecollagenase II in the composition is about 0.35 to about 0.45.